During the polymerization of monomers, considerable amounts of unreacted monomer were found to be entrapped in the polymers. Polymerization is a complex multistage process. In addition to entrapped unreacted monomer, dimeric, trimeric and other low molecular weight compounds may similarly be entrapped. Some of these compounds may leave the polymer by subsequent diffusion and thus lead to a substantial concentration on the environment under the conditions of polymer processing. These low molecular weight compounds may have properties as hazardous as those associated with monomer. In the past several months, we have studied the polymerization of acrylamide, acrylonitrile, styrene and vinyl chloride under various conditions. It was found that in all cases, significant amounts of unreacted monomer were trapped with polymers produced. The diffusion rate of entrapped monomer out of the polymer depends on the nature of the polymer product, e.g., molecular weights, their distributions and degree of crosslinking. Preliminary results show that the rate of diffusion of entrapped monomers are in the order of vinyl chloride greater than styrene greater than acrylonitrile greater than acrylamide. We have also found that low molecular weight components such as dimeric and trimeric species were produced and entrapped in the polymer produced. The detailed investigation on the formation of low molecular weight compounds of these monomers and their diffusibilities in polymer products are being carried forward.